1. Field of the Invention
The present invention relates to a driving device which drives an optical member by means of a driving source and also allows the optical member to be driven by a manual operation, as well as to an optical apparatus having such driving device.
2. Description of Related Art
A lens barrel of the type which includes a built-in vibration type motor has heretofore been used. This type of lens barrel is arranged to perform an automatic focusing operation by means of a ring-shaped vibration type motor built in the lens barrel and also to allow a user to perform a manual focusing operation without the need for a special changeover operation.
A planetary mechanism type of driving device for such lens barrel is proposed in, for example, Japanese Laid-Open Patent Application No. Hei 2-253216 (U.S. Pat. No. 5,335,115). The planetary mechanism type of driving device includes a power transmitting member for transmitting the driving force of a vibration type motor, an operating force transmitting member for transmitting a driving force for manual operation, and planetary rollers maintained in contact with these transmitting members, and rotating support shafts for the respective planetary rollers are provided on an output member which performs lens driving.
FIG. 4 shows one example of the planetary mechanism type of lens driving device for the lens barrel. Referring to FIG. 4, a support tube 101 serves to hold various constituent components of the lens driving device. A ring-shaped vibrator (hereinafter referred to as a stator) 102 constitutes part of a vibration type motor, and an electromechanical energy converting element 103 is joined to one end surface of the stator 102 to excite a vibration in the stator 102. A vibration absorber 104 such as felt is maintained in pressure contact with one surface of the electro-mechanical energy converting element 103, and a disc spring 105 is provided for urging the vibration absorber 104 and the stator 102 in the forward direction along the optical axis of the lens barrel (in FIG. 4, toward the left).
A nut 106 for adjusting the pressure of the disc spring 105 is screwed onto a threaded portion formed to extend around the outer diameter portion of the support tube 101, and a rotation stopper 107 for inhibiting the rotation of the stator 102 is integrally held on the outer diameter portion of the support tube 101. A rotor 108 is arranged to receive a rotating force about the optical axis from the stator 102 while the stator 102 is vibrating, and an automatic-focusing connection plate 110 is arranged to rotate integrally with the rotor 108 via a rubber ring 109.
An output rotating tube 111 has a plurality of shafts 111a which extend in radial directions centered at the optical axis, and rollers 112 are rotatably secured to the shafts 111a, respectively. A focusing key 115 for transmitting the rotation of the output rotating tube 111 to a cam ring for lens driving (not shown) is secured to the output rotating tube 111. A manual-focusing connection plate 113 is arranged to rotate together with a manual operating member (not shown).
Each of the rollers 112 is disposed between the automatic-focusing connection plate 110 and the manual-focusing connection plate 113 and is maintained in contact with both plates 110 and 113. For example, if the driving force of the vibration type motor is transmitted to the automatic-focusing connection plate 110 and the automatic-focusing connection plate 110 is rotated about the optical axis, the rollers 112 revolve about the optical axis together with the output rotating tube 111 while each of the rollers 112 is rotating on its axis, since the rotation of the manual-focusing connection plate 113 is inhibited by the friction between the manual-focusing connection plate 113 and the lens barrel through the manual operating member. The rotation of the output rotating tube 111 is transmitted to the cam ring through the focusing key 115, and a lens (not shown) is driven to move along the optical axis by the cam ring.
On the other hand, if a driving force from the manual operating member is transmitted to the manual-focusing connection plate 113 and the manual-focusing connection plate 113 is rotated about the optical axis, since the rotation of the automatic-focusing connection plate 110 is inhibited by friction between the rotor 108 and the stator 102 of the vibration type motor, the rollers 112 revolve about the optical axis together with the output rotating tube 111 while each of the rollers 112 is rotating on its axis, and the rotation of the output rotating tube 111 is transmitted to the cam ring through the focusing key 115 and the lens is driven to move along the optical axis by the cam ring.
In this manner, it is possible to drive the lens without performing a special changeover operation, merely by actuating the vibration type motor or operating the manual operating member.
In the field of such lens driving device, there is not much demand for higher lens-driving speeds with respect to the operating speed of the manual operating member, because it is necessary for users to readily make fine adjustment of a lens position (focus). In contrast, there is an increasing demand for higher lens-driving speeds for automatic focusing.
In the above-described conventional lens barrel, the driving force of the vibration type motor is transmitted to the output member after having been speed-reduced by the planetary mechanism. If the speed of transmission to the output member is to be increased to make the speed of automatic focusing far higher, the driving speed of the vibration type motor may be made faster. However, as the driving speed of the vibration type motor is made faster, it becomes more difficult to control the stop position of the vibration type motor, and this leads to the problem that the accuracy of control of automatic focusing is easily impaired.
In the lens barrel shown in FIG. 4, the pressure produced by the disc spring 105 to press the stator 102 against the rotor 108 in the vibration type motor is utilized to maintain each of the rollers 112 in pressure contact with both connection plates 110 and 113. Accordingly, care must be taken to optimally set both the pressure between the stator 102 and the rotor 108 and the pressure between each of the rollers 112 and both connection plates 110 and 113.
There is a recently proposed type of lens barrel which makes use of a differential mechanism which uses rollers as a planetary mechanism. The respective rollers of the planetary mechanism have rotating shafts in radial directions perpendicular to the optical axis of the lens barrel. The rollers of the planetary mechanism are disposed in the state of being clamped between an output end surface associated with a manual ring for manual focusing and an output end surface associated with a vibration type motor (ultrasonic motor) for automatic focusing, and an output ring arranged to rotate with the revolution of the rollers about the optical axis is disposed to constitute a differential mechanism whose final output is the rotation of the output ring.
In order to prevent an excessive force from acting on the differential mechanism even if the manual ring is rotated when the rotation of the output ring is inhibited, a friction coefficient is set so that the rollers and the output end surface associated with the manual ring can start slipping at any time when the manual ring is rotated with the rotation of the output ring being inhibited.
Incidentally, if the rollers and the output end surface of the rotor of the vibration type motor are arranged to start slipping at an earlier timing, the rollers rotate about their respective axes without rolling on the output end surface of the rotor and the output end surface of the rotor is abraded at particular points only, so that the marks of the abrasion will be made on the output end surface. On the other hand, if the rollers and the output end surface associated with the manual ring are arranged to start slipping at an earlier timing, the rollers do not roll nor rotate and only the manual ring rotates, so that the entire output end surface associated with the manual ring will be abraded by the rollers. Accordingly, the latter arrangement is more advantageous in abrasion than the former arrangement.
In addition, since the output ring is arranged to drive a focusing lens, the feature of the structure of the ultrasonic motor can be fully utilized, particularly during a manual focusing operation.
As is known, in the vibration type motor, a ring-shaped rotor which constitutes an output member is maintained in pressure contact with a ring-shaped metallic elastic body (which corresponds to a stator) in which to form a progressive wave, by a pressure member such as a spring, so that the rotor is frictionally driven by the progressive wave formed in the elastic body.
In the above-described differential mechanism, even if the output member rotates which receives the pressure of the pressure member along the optical axis, the pressure of the pressure member acts so that the manual ring maintains a non-rotating state, whereas if the manual ring is rotated to perform manual focusing, the non-rotating state of the rotor is maintained because the rotor of the vibration type motor is maintained in pressure contact with the stator. Accordingly, it is possible to effect changeover between an automatic focusing operation and a manual focusing operation without using a special changeover mechanism.
In the conventional lens barrel having the above-described structure, the rollers are used as the planetary mechanism in the differential mechanism which effects changeover between the manual focusing operation and the automatic focusing operation without a special changeover operation, and the output end surface of the vibration type motor and the output end surface of the manual ring are maintained in frictional contact with each other with the rollers being clamped therebetween, thereby realizing transmission of a driving force. Since the pressure of the pressure member for pressing the rotor against the stator of the vibration type motor is used as the pressure required for such frictional contact, such pressure is set to an optimum pressure which can bring out the performance of the vibration type motor.
For this reason, if a focusing lens having a large lens load is driven, a slip occurs in the frictional contact with the rollers and it becomes impossible to efficiently transmit the output of the vibration type motor, so that the focusing lens may not be fully driven.
To cope with this problem, it is preferable that the friction coefficient between the rollers and the output end surface of the manual ring be increased within a range smaller than the friction coefficient between the rollers and the output end surface of the rotor of the vibration type motor, because the first slip occurs between the rollers and the output end surface of the manual ring. However, it is difficult to continuously vary the friction coefficient which greatly depends on the materials of the surfaces in contact with each other.
For this reason, to efficiently transmit the output of the vibration type motor, a pressure member for raising the driving force to a limit driving force capable of transmitting drive without causing a slip between the outer circumferential surface of each of the rollers and the output end surfaces of both the manual ring and the vibration type motor (hereinafter referred to as a slip torque) is provided separately from the pressure member for pressing the rotor against the stator of the vibration type motor, thereby applying to the vibration type motor an optimum pressure capable of bringing out the performance of the vibration type motor.
It has also been proposed to provide an arrangement which makes it possible to apply a pressure capable of producing a sufficient slip torque for the frictional contact between the outer circumferential surface of each of the rollers and the output end surfaces of both the manual ring and the vibration type motor (hereinafter referred to as a pressure separating type).
One conventional example of the pressure separating type will be described below with reference to FIG. 9.
FIG. 9 is a diagrammatic cross-sectional view of a conventional focusing driving unit. A unit support tube 301 serves to hold various constituent components of the focusing driving unit. A ring-shaped vibrator (hereinafter referred to as a stator) 302 has a trapezoidal shape in cross section, and an electrostrictive element 303 for vibrating the stator 302 is joined to one end surface of the stator 302.
A ring-shaped vibration absorber 304 made of felt or the like is maintained in pressure contact with one surface of the electrostrictive element 303, and a first disc spring 305 constitutes first pressure means for urging the vibration absorber 304 along the optical axis of the lens barrel. A first nut 306 for adjusting the pressure of the disc spring 305 is screwed into a threaded portion formed to extend around the inner diameter portion of the unit support tube 301.
A rotation stopper 307 for inhibiting the rotation of the stator 302 is integrally held on the inner diameter portion of the unit support tube 301. A rotor 308 serves as a contact element arranged to receive a rotating force about the optical axis from the stator 302, and a first connection plate 310 is arranged to rotate integrally with the rotor 308 via a rubber ring 309 and is maintained in contact with a first roller 312 which will be described later.
A plurality of roller support shafts 311 each of which rotatably supports the first roller 312 and a second roller 313 (to be described later) are secured to the unit support tube 301 in such a manner as to project toward the optical axis from the inner diameter portion of the unit support tube 301. The first roller 312 is maintained in contact with the first connection plate 310 to receive pressure from first pressure means 305, and has a bearing structure formed by two separate inner and outer diameter sides which are joined to each other by bearing balls to eliminate rotational loss.
The second roller 313 is maintained in contact with a second connection plate 314 (which will be described later) and receives pressure from second pressure means (which will be described later), and has a bearing structure formed by two separate inner and outer diameter sides which are joined to each other by bearing balls to eliminate rotational loss. The second connection plate 314 is maintained in contact with a third roller (which will be described later) and is pressed by the second pressure means and is engaged with a claw of the first connection plate 310 so that the rotation of the first connection plate 310 is transmitted to the second connection plate 314 and the second connection plate 314 is rotated in the same direction as the first connection plate 310.
An output ring 315 has a plurality of output shafts 315a which extend in radial directions centered at the optical axis, and third rollers 316 which will be described later are rotatably supported by the output shafts 315a, respectively. The revolution of the third rollers 316 about the optical axis is transmitted to the output ring 315, and the rotation of the output ring 315 is transmitted to a cam ring (not shown) connected to the output ring 315. The third rollers 316 are rotatably supported by the output ring 315, and revolve about the optical axis while rolling in the state of being clamped between the second connection plate 314 and a manual-focusing connection plate 317 which will be described later.
The rotation of a focusing ring (not shown) is transmitted to the manual-focusing connection plate 317, and the manual-focusing connection plate 317 receives pressure from the second pressure means (which will be described later) and one end surface of the manual-focusing connection plate 317 is maintained in contact with the third rollers 316.
The material of the manual-focusing connection plate 317 is selected so that the friction coefficient between the third rollers 316 and the manual-focusing connection plate 317 becomes smaller than the friction coefficient between the third rollers 316 and the second connection plate 314. A holding ring 318 is pressed by the second pressure means (which will be described later) and is maintained in contact with the manual-focusing connection plate 317, and is fitted on the body of the focusing driving unit to inhibit the rotation of the body.
A reinforcement plate 319 is secured to the holding ring 318. A second disc spring 320 constitutes the second pressure means, and urges the manual-focusing connection plate 317 against the third rollers 316 along the optical axis. A second nut 321 for adjusting the pressure of the second disc spring 320 is screwed into a threaded portion formed to extend around the inner diameter portion of the unit support tube 301.
However, in the conventional pressure separating type, pressure separating parts for respectively receiving pressure from the vibration type motor and pressure from the manual ring (in the conventional example, the first rollers 312 and the second rollers 313) are disposed in parallel along the optical axis between a vibration type motor portion and a manual connection portion, so that the thrust length of the unit increases.
To obtain another means for solving the above-described problem, attention has been paid to the fact that the slip torque due to the frictional contact between the outer circumferential surface of each of the rollers and the output end surface of the manual ring is smaller than the slip torque due to the frictional contact between the outer circumferential surface of each of the rollers and the output end surface of the vibration type motor and a slip starts to occur at all times between the outer circumferential surface of each of the rollers and the output end surface of the manual ring.
A driving unit, which is incorporated in a lens barrel including a built-in vibration type motor composed of a ring-shaped stator and rotor disposed concentrically with the optical axis of a lens, is provided with a manual-focusing connection member to which the rotation of a manual ring is to be transmitted, and first rollers which are disposed at at least three circumferential locations centered at the optical axis of the lens and which are respectively rotatable on radial axes perpendicular to the optical axis and are capable of rolling in the state of being clamped between the rotor of the vibration type motor and the manual-focusing connection member.
The driving unit also includes an output ring which rotatably supports the first rollers and which rotates about the optical axis by receiving a revolution of the first rollers about the optical axis, a first pressure member which maintains end surfaces of the rotor and the stator of the vibration type motor in pressure contact with each other and also the outer circumferential surfaces of the first rollers and the end surface of the rotor in pressure contact with each other, a second pressure member which maintains the outer circumferential surfaces of the first rollers and an end surface of the manual-focusing connection member in pressure contact with each other, and second rollers which are disposed on the output ring and are urged against an end surface of a fixed portion by the pressure of the second pressure member via the first roller and the output ring.
In the above-described proposed arrangement, the slip torque due to the frictional contact between the outer circumferential surfaces of the rollers and the output end surface of the manual ring can be adjusted to a largest value within a range smaller than the slip torque due to the frictional contact between the outer circumferential surfaces of the rollers and the output end surface of the vibration type motor, whereby the thrust size of the driving unit can be shortened.
One example of the above-described proposed arrangement will be described below with reference to FIG. 10.
FIG. 10 is a diagrammatic cross-sectional view of a focusing driving unit. A unit support tube 401 serves to hold various constituent components of the focusing driving unit. A ring-shaped vibrator (hereinafter referred to as a stator) 402 has a trapezoidal shape in cross section, and an electrostrictive element 403 for vibrating the stator 402 is joined to one end surface of the stator 402. A ring-shaped vibration absorber 404 made of felt or the like is maintained in pressure contact with one surface of the electrostrictive element 403.
A first disc spring 405 constitutes first pressure means for urging the vibration absorber 404 along the optical axis of the lens barrel. A first nut 406 for adjusting the pressure of the disc spring 405 is screwed into a threaded portion formed to extend around the inner diameter portion of the unit support tube 401. The pressure of the first pressure means (the disc spring) 405 is adjusted to an optimum pressure which is capable of bringing out the maximum performance of the vibration type motor.
A rotation stopper 407 for inhibiting the rotation of the stator 402 is integrally held on the inner diameter portion of the body of the focusing driving unit. A rotor 408 is arranged to receive a rotating force about the optical axis of the lens barrel, due to a vibration wave produced in the stator 402.
A connection plate 410 is arranged to rotate integrally with the rotor 408 via a rubber ring 409 and is maintained in contact with first rollers 412 which will be described later.
An output ring 411 has a plurality of shafts 411a and 411b which extend approximately equally in radial directions centered at the optical axis, and the respective shafts 411a rotatably support the first rollers 412 which will be described later, while the respective shafts 411b rotatably support second rollers 413 which will be described later. The rotation of the output ring 411 is transmitted to a cam ring (not shown) which is connected to the output ring 411.
The respective first rollers 412 are rotatably supported by the shafts 411a disposed at a plurality of locations on the output ring 411, and revolve about the optical axis while rolling in the state of being clamped between the connection plate 410 and a manual-focusing connection plate 414. The respective second rollers 413 are rotatably supported by the shafts 411b disposed at a plurality of locations on the output ring 411, and are urged against an end surface of an inner diameter projection 401a of the unit support tube 401 by receiving the pressure applied by second pressure means (which will be described later) from the manual-focusing connection plate 414 (which will be described later) through the first rollers 412 and the output ring 411. The second rollers 413 have a bearing structure formed by two separate inner and outer diameter sides which are joined to each other by bearing balls to eliminate rotational loss.
The second rollers 413 are disposed on the output ring 411 at the same locations as the first rollers 412 in the direction of the optical axis and out of phase with the same in the radial directions so that the second rollers 413 do not interfere with the first rollers 412. The rotation of a focusing ring (not shown) is transmitted to the manual-focusing connection plate 414, and one end surface of the manual-focusing connection plate 414 is maintained in contact with the first rollers 412 by receiving pressure from the second pressure means which will be described later.
The material of the manual-focusing connection plate 414 is selected so that the friction coefficient between the first rollers 412 and the manual-focusing connection plate 414 is smaller than the friction coefficient between the first rollers 412 and the connection plate 410. A holding ring 415 is pressed by the second pressure means (which will be described later) and is maintained in contact with the manual-focusing connection plate 414. The holding ring 415 is fitted on the unit support tube 401 to inhibit the rotation thereof.
A reinforcement plate 416 is secured to the holding ring 415. A second disc spring 417 constitutes the second pressure means, and urges the manual-focusing connection plate 414 against the first rollers 412 along the optical axis.
A second nut 418 for adjusting the pressure of the second disc spring 417 is screwed into a threaded portion formed to extend around the inner diameter portion of the body of the focusing driving unit. The pressure of the second pressure means (the second disc spring) 417 is adjusted to a pressure larger than that of the first pressure means (the first disc spring) 405 so that slip torque due to the frictional contact between the first rollers 412 and an end surface of the manual-focusing connection plate 414 becomes as large as possible within a range smaller than slip torque due to the frictional contact between the first rollers 412 and the connection plate 410.
However, even in the above proposal, the value of output torque is limited because the slip torque on the side of the manual-focusing connection plate 414 is merely increased within the range of the slip toque on the side of the vibration type motor, which slip torque is predetermined on the basis of the pressure of the vibration type motor.